Chop* onion. Heat oil in a large saucepan over medium-low heat and add onion. Cook and stir while you continue.
Chop celery, optional red pepper, and garlic. Add to onion. Cook and stir an additional 2 to 3 minutes.
Stir in cumin, ginger, paprika, and pepper. Cook 1 minute.
Add 4 cups water (or broth) and turn heat up to medium-high.
Sort lentils: Measure then spread onto a plate or cutting board. Discard any pieces of pebbles, grains, or discolored lentils. Rinse lentils in a colander to remove sand or grit, then add to saucepan. Bring to a gentle boil. Turn heat down to keep at a simmer (uncovered) about 15 minutes, or until lentils are soft.
Drain and rinse chickpeas. Add to soup along with tomato sauce and salt. Add up to 1 additional cup of water (or broth) if desired. Cook 30 minutes. NOTE: Can serve right away or cook longer, which intensifies flavor.
Chop parsley (or cilantro). Remove soup from heat and stir in parsley, cinnamon, and lemon juice. Add hot sauce if desired.
*Tip: Tomato paste is a great flavor-enhancer that adds a little sweetness and color to this soup. We keep a tube of tomato paste in the refrigerator for recipes like this one, but the soup will be fine without tomato paste if you don't have any.
*Technique: How to Slice or Dice Onions – Cut off stem end to create a flat surface. Place on a cutting board and slice in half. Remove papery peeling (and the next layer if tough or slippery). Place cut-side down on the cutting board and slice off root end. Hold onion half with thumb on one side and fingers on the other, with your palm arched up over the onion. Bring the knife under the palm of that hand and start carefully slicing as you hold it together. To chop, rotate and do the same thing in the other direction.
Garnish with additional parsley (or cilantro) and a dollop of Greek yogurt if desired. Serve with crackers or toast, and fruit or green salad.